1. Field of the Invention
This invention relates generally to a cannula used as an aid for insertion of catheters and other instruments into the body and more particularly to a cannula which abuts a ledge or spur located on or near the distal end of a dilator so as to provide a smooth transition between the sheath and the dilator and to a method for making the dilator-sheath assembly.
2. Brief Description of the Background
It is a frequent practice when introducing balloon, electrode, closed end, and other catheters or instruments into the body, to first introduce a cannula or sheath to aid in the introduction of the catheter or other instruments. Frequently the cannula or sheath will be placed on a dilator which is used on a wire guide to dilate a puncture made by a needle. It is desirable when inserting the dilator that the dilator's outside surface be as smooth as possible in order to prevent patient discomfort. To make insertion of the cannula or sheath as atraumatic as possible, it is also important that the transitions between the dilator and the cannula or sheath be as even as possible.
The current design of introducer systems includes a dilator, or dummy catheter, which is surrounded by the sheath. The sheath is frequently made of thin walled Teflon, although other materials may be used. Typically, the distal end of the sheath is tapered and fitted to the dilator. However, the fit of the sheath onto the dilator does not always create a transition which is smooth enough so that the dilator and sheath will pass easily through the tissue. Therefore, whenever fibrous tissue is encountered during the introduction of the sheath dilator combination, some resistance is encountered when the transition between the dilator and sheath is advanced through the tissue. In some cases, the distal end of the sheath is damaged during advancement through fibrous tissue. As advancement continues, the deformed sheath tip becomes harder to advance because of tearing and flaring, damaging the tissue and creating more trauma to the patient.
The present invention provides a dilator to sheath transition which is smooth, thus preventing undue trauma upon insertion into the patient.